机械密封冷却水温度升高超过（）℃时，能够引起给水泵跳闸。
参考答案：80
When Mr Wang was young, he________ in the river.
A．uses to swim
B．used to swim
C．used to swimming
D．used swim
正六边形的半径为6cm，它的中心角等于______，边长为______，边心距等于______．
